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2.3 - Quality Standards : Noise & Color Distortion
Digital Noise & Color Distortion: Image noise is the variation of values in the detection process of your camera. Noise and color distortion (or digital noise) occurs most frequently in uniform color areas (i.e. skies and shadows) and is caused by temperature and/or sensitivity/ISO settings. With increased sensitivity, more light is required to avoid producing noise. With long exposures, cameras can also produce a different category of noise called hot pixels (stand alone color dots/pixels).
Noise Correction: The key to noise reduction (by either spot editing or noise filters and programs, such as Neat Image and Noise Ninja) is to correct the problem areas without affecting the overall quality and detail of the image. Freeware programs tend to produce lower quality results by creating a blanket "watercolor" or blurred effect and can also have limited settings for saving in highest quality.
Compression: The JPEG file format uses a "lossy" compression method, in order to make the file smaller information is thrown away, or lost. The "quality" setting that most image editing programs and digital cameras have when saving JPEGs determines how much information is lost. At a certain point, with lower quality settings, the removal of information during the compression process can become visible in the form of compression artifacts (places in the image where too much detail has been lost). Too much JPEG compression can become visible either in the form of a general loss of detail, or grainy/patterned areas (especially in flat spaces, such as skies).
Artifacting: Compression artifacting can be introduced by the camera and/or by your image editing software at lower quality settings. Also, re-sizing, re-sampling, and re-saving can all degrade the quality of a JPEG image, so one should be careful about re-saving JPEGs. If for example, a photo was re-saved 4 times (even at a quality of "12" or "Best") the image quality will become worse and worse. With this in mind, it is obviously best to start with the cleanest image possible. You may want to double-check your camera settings to make sure it is saving at the highest quality.
Original Image
The above is an example of an acceptable image. Viewed at 100%, there is no visible noise, pixel discoloration, or "jaggies" caused by too much JPG compression.
Do Not Submit:
Noise (and pixel/color distortion)
Possible Solution: Adjust the ISO settings of your camera to 200 ISO or slower. Alternately, use slower speed film (25 to 200 ISO) for the least amount of noise and/or film grain.
Compression (*jaggies)
Possible Solution: Save your original image at a higher quality level (9-12 is optimal). Also, re-sizing, re-sampling, and re-saving can all degrade the quality of a JPG image, so one should be careful about re-saving JPGs.
Tips:
- Always save images at 100% quality
- Some images have too high levels of noise to be corrected by noise filters/programs
- The higher the ISO setting the more light needed to avoid noise
- Some post editing programs can create noise once resaved
- Every part of a photo needs a different amount of adjusting to get rid of noise, etc.
- Post edit images in TIFF (or PSD) format to avoid compression
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